Effect of accounting for interfractional CTV shape variations in PTV margins on prostate cancer radiation treatment plans |
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| Institution: | 1. Graduate School of Medical Sciences, Kyushu University, 3-1-1, Maidashi, Higashi-ku, Fukuoka 812-8582, Japan;2. Faculty of Medical Sciences, Kyushu University, 3-1-1, Maidashi, Higashi-ku, Fukuoka 812-8582, Japan;3. Kyushu University Hospital, 3-1-1, Maidashi, Higashi-ku, Fukuoka 812-8582, Japan;1. Cancer Prognostics and Health Outcomes Unit, University of Montreal Health Center, Montreal, Quebec, Canada;2. Martini-Clinic, Prostate Cancer Center Hamburg-Eppendorf, Hamburg, Germany;3. Department of Urology, University of Montreal Health Center, Montreal, Quebec, Canada;4. Department of Urology and Division of Experimental Oncology, URI, Urological Research Institute, IRCCS San Raffaele Scientific Institute, Milan, Italy;5. Department of Urology, Academic Hospital Braunschweig, Braunschweig, Germany;6. Institute of Pathology, University Medical Center Hamburg-Eppendorf, Hamburg, Germany;1. Department of Radiation Oncology, University of Miami Miller School of Medicine, Miami, Florida;2. Department of Radiation Oncology, University of California, Los Angeles, Los Angeles, California;2. RMIT University, Melbourne, Australia;3. Radiation Therapy Services, Peter MacCallum Cancer Centre, Melbourne, Australia;1. Department of Radiation Oncology, University of Miami, 1475 NW 12th Ave, Suite 1500, Miami, FL 33136, United States;2. Radiation Oncology and Diagnostic Imaging, H. Lee Moffitt Cancer Center, 12902 Magnolia Dr., Tampa, FL 33612, United States;1. Istituto Nazionale di Fisica Nucleare, Laboratori Nazionali del Sud, Via Santa Sofia 62, Catania, Italy;2. School of Mathematics and Physics, Queens University Belfast, United Kingdom;3. Physics and Astronomy Department, University of Catania, Via S. Sofia 64, Catania, Italy;4. Institute of Physics ASCR, v.v.i (FZU), ELI-Beamlines Project, 182 21 Prague, Czech Republic;5. National Physical Laboratory, CMES – Medical Radiation Science Hampton Road, Teddington, Middlesex, TW11 0LW UK;1. Department of Radiotherapy and Radiation Oncology, University of Marburg, Germany;2. Department of Medical Physics in Radiation Oncology, German Cancer Research Center (DKFZ), Heidelberg, Germany |
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| Abstract: | PurposeThe aim of this study was to account for interfractional clinical target volume (CTV) shape variation and apply this to the planning target volume (PTV) margin for prostate cancer radiation treatment plans.MethodsInterfractional CTV shape variations were estimated from weekly cone-beam computed tomography (CBCT) images using statistical point distribution models. The interfractional CTV shape variation was taken into account in the van Herk’s margin formula. The PTV margins without and with the CTV shape variation, i.e., standard (PTVori) and new (PTVshape) margins, were applied to 10 clinical cases that had weekly CBCT images acquired during their treatment sessions. Each patient was replanned for low-, intermediate-, and high-risk CTVs, using both margins. The dose indices (D98 and V70) of treatment plans with the two margins were compared on weekly pseudo-planning computed tomography (PCT) images, which were defined as PCT images registered using a deformable image registration technique with weekly CBCT images, including contours of the CTV, rectum, and bladder.ResultsThe percentage of treatment fractions of patients who received CTV D98 greater than 95% of a prescribed dose increased from 80.3 (PTVori) to 81.8% (PTVshape) for low-risk CTVs, 78.8 (PTVori) to 87.9% (PTVshape) for intermediate-risk CTVs, and 80.3 (PTVori) to 87.9% (PTVshape) for high-risk CTVs. In most cases, the dose indices of the rectum and bladder were acceptable in clinical practice.ConclusionThe results of this study suggest that interfractional CTV shape variations should be taken into account when determining PTV margins to increase CTV coverages. |
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| Keywords: | Shape variation PTV margin Treatment planning Prostate cancer radiation therapy |
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